Liquid oxygen

Short description: One of the physical forms of elemental oxygen

"LOX" redirects here. For other uses, see Lox (disambiguation).

Liquid oxygen (O
2) (cyan liquid) in a beaker. When liquid oxygen (O
2) is poured from a beaker into a strong magnet, the oxygen is temporarily suspended between the magnet poles, owing to its paramagnetism.

Liquid oxygen, sometimes abbreviated as LOX or LOXygen, is a clear, pale cyan liquid form of dioxygen O
2. It was used as the oxidizer in the first liquid-fueled rocket invented in 1926 by Robert H. Goddard,[1] an application which is ongoing.

## Contents

* 1 Physical properties
* 2 Uses
* 2.1 In rocket propellant
* 3 History
* 4 See also
* 5 References
* 6 Further reading

## Physical properties

Liquid oxygen has a clear, pale cyan color and is strongly paramagnetic: it can be suspended between the poles of a powerful horseshoe magnet.[2] Liquid oxygen has a density of 1.141 kg/L (1.141 g/ml), slightly denser than liquid water, and is cryogenic with a freezing point of 54.36 K (−218.79 °C; −361.82 °F) and a boiling point of 90.19 K (−182.96 °C; −297.33 °F) at 1 bar (14.5 psi). Liquid oxygen has an expansion ratio of 1:861[3][4] and because of this, it is used in some commercial and military aircraft as a transportable source of breathing oxygen. Liquid oxygen is also a very powerful oxidizing agent: organic materials will burn rapidly and energetically in liquid oxygen. Further, if soaked in liquid oxygen, some materials such as coal briquettes, carbon black, etc., can detonate unpredictably from sources of ignition such as flames, sparks or impact from light blows. Petrochemicals, including asphalt, often exhibit this behavior.[5]

The tetraoxygen molecule (O4) was predicted in 1924 by Gilbert N. Lewis, who proposed it to explain why liquid oxygen defied Curie's law.[6] Modern computer simulations indicate that, although there are no stable O4 molecules in liquid oxygen, O2 molecules do tend to associate in pairs with antiparallel spins, forming transient O4 units.[7]

The surface tension of liquid oxygen at its normal pressure boiling point is 13.2 dyn/cm (13.2 mN/m).[8]

## Uses

A U.S. Air Force technician transfers liquid oxygen to a Lockheed Martin C-130J Super Hercules aircraft at the Bagram Airfield, Afghanistan. Liquid oxygen tank at National Hospital (Teaching), Kandy Insulated evaporator and storage container setup for liquid oxygen

Air forces have long recognized the strategic importance of liquid oxygen, both as an oxidizer and as a supply of gaseous oxygen for breathing in hospitals and high-altitude aircraft flights. In 1985, the USAF started a program of building its own oxygen-generation facilities at all major consumption bases.[9][10]

### In rocket propellant

See also: Engineering:Liquid rocket propellant

SpaceX's liquid oxygen ball at Cape Canaveral

Liquid oxygen is the most common cryogenic liquid oxidizer propellant for spacecraft propulsion applications, usually in combination with liquid hydrogen, kerosene or methane.[11][12]

As of 2026, many active rockets use liquid oxygen:

* Chinese space program
* CASC: Long March (rocket family)
* operational: Long March -5, -5B, -6, -6A, -6C, -7, -7A, -8, -8A, -12, -12A
* under development: -9, -10, -10A, -10B, -12B
* CAS Space: Kinetica 2 (under development)
* Deep Blue Aerospace: Nebula-1 (under development)
* Galactic Energy: Pallas-1 (under development)
* i-Space: Hyperbola-3 (under development)
* LandSpace: Zhuque-2E, Zhuque-3
* Orienspace: Gravity-2 (under development)
* Space Epoch: Yuanxingzhe-1 (under development)
* Space Pioneer: Tianlong-2, Tianlong-3 (under development)
* Europe
* European Space Agency: Ariane 6
* Isar Aerospace: Spectrum (under development)
* Rocket Factory Augsburg: RFA One (under development)
* Indian Space Research Organisation: GSLV, LVM3
* JAXA (Japan): H3
* Korea Aerospace Research Institute: Nuri
* Roscosmos (Russia): Soyuz-2, Angara, Irtysh (under development)
* United States
* Blue Origin: New Shepard, New Glenn
* Firefly Aerospace: Firefly Alpha
* NASA: Space Launch System
* Northrop Grumman: Antares 300 (under development)
* Rocket Lab: Electron, Neutron (under development)
* SpaceX: Falcon 9, Falcon Heavy, Starship
* Stoke Space: Nova (under development)
* United Launch Alliance: Atlas V, Vulcan

## History

* By 1845, Michael Faraday had managed to liquefy most gases then known to exist. Six gases, however, resisted every attempt at liquefaction[13] and were known at the time as "permanent gases". They were oxygen, hydrogen, nitrogen, carbon monoxide, methane, and nitric oxide.
* In 1877, Louis Paul Cailletet in France and Raoul Pictet in Switzerland succeeded in producing the first droplets of liquid air.[14]
* In 1883, Polish professors Zygmunt Wróblewski and Karol Olszewski produced the first measurable quantity of liquid oxygen.[15]

## See also

* Oxygen storage
* Industrial gas
* Cryogenics
* Liquid hydrogen
* Liquid helium
* Liquid nitrogen
* List of stoffs
* Natterer compressor
* Rocket fuel
* Solid oxygen
* Tetraoxygen

## References

1. ↑ "First liquid-fueled rocket" (in en). https://www.history.com/this-day-in-history/first-liquid-fueled-rocket.
2. ↑ Moore, John W.; Stanitski, Conrad L.; Jurs, Peter C. (21 January 2009). Principles of Chemistry: The Molecular Science. Cengage Learning. pp. 297–. ISBN 978-0-495-39079-4. https://books.google.com/books?id=ZOm8L9oCwLMC&pg=PA297. Retrieved 3 April 2011.
3. ↑ Cryogenic Safety. chemistry.ohio-state.edu.
4. ↑ Characteristics. . Lindecanada.com. Retrieved on 2012-07-22.
5. ↑ "Liquid Oxygen Receipt, Handling, Storage and Disposal". USAF Training Film. https://archive.org/details/23004LiquidOxygenReceiptTransferStorageDisposal.
6. ↑ Lewis, Gilbert N. (1924). "The Magnetism of Oxygen and the Molecule O2". Journal of the American Chemical Society 46 (9): 2027–2032. doi:10.1021/ja01674a008.
7. ↑ Oda, Tatsuki; Alfredo Pasquarello (2004). "Noncollinear magnetism in liquid oxygen: A first-principles molecular dynamics study". Physical Review B 70 (134402): 1–19. doi:10.1103/PhysRevB.70.134402. Bibcode: 2004PhRvB..70m4402O. https://kanazawa-u.repo.nii.ac.jp/?action=repository_uri&item_id=10177.
8. ↑ J. M. Jurns and J. W. Hartwig (2011). Liquid Oxygen Liquid Acquisition Device Bubble Point Tests With High Pressure LOX at Elevated Temperatures, p. 4.
9. ↑ Arnold, Mark. 1U.S. Army Oxygen Generation System Development. RTO-MP-HFM-182. dtic.mil
10. ↑ Timmerhaus, K. D. (8 March 2013). Advances in Cryogenic Engineering: Proceedings of the 1957 Cryogenic Engineering Conference, National Bureau of Standards Boulder, Colorado, August 19–21, 1957. Springer Science & Business Media. pp. 150–. ISBN 978-1-4684-3105-6. https://books.google.com/books?id=LVfaBwAAQBAJ&pg=PA150.
11. ↑ Belluscio, Alejandro G. (March 7, 2014). "SpaceX advances drive for Mars rocket via Raptor power". NASAspaceflight.com. http://www.nasaspaceflight.com/2014/03/spacex-advances-drive-mars-rocket-raptor-power/.
12. ↑ Todd, David (November 20, 2012). "Musk goes for methane-burning reusable rockets as step to colonise Mars". FlightGlobal Hyperbola. http://www.flightglobal.com/blogs/hyperbola/2012/11/musk-goes-for-methane-burning.html. ""We are going to do methane," Musk announced as he described his future plans for reusable launch vehicles including those designed to take astronauts to Mars within 15 years. "The energy cost of methane is the lowest and it has a slight Isp (Specific Impulse) advantage over Kerosene" said Musk adding, "and it does not have the pain in the ass factor that hydrogen has." ... SpaceX's initial plan will be to build a lox/methane rocket for a future upper stage codenamed Raptor. ... The new Raptor upper stage engine is likely to be only the first engine in a series of lox/methane engines."
13. ↑ Cryogenics. Scienceclarified.com. Retrieved on 2012-07-22.
14. ↑ Papanelopoulou, Faidra (2015). Louis Paul Cailletet, the Liquefaction of Oxygen and the Emergence of an `In-Between Discipline': Low-Temperature Research. Springer International Publishing. pp. 9-22. ISBN 978-3-319-14553-2. https://doi.org/10.1007/978-3-319-14553-2_2.
15. ↑ Kubbinga, Henk (2010), "A Tribute to Wróblewski and Olszewski", Europhysics News 41 (4): 21-24, doi:10.1051/epn/2010402, https://www.europhysicsnews.org/10.1051/epn/2010402/pdf

## Further reading

* Schmidt, Eckart W. (2022). "Oxygen". Encyclopedia of Oxidizers. De Gruyter. pp. 3053–3218. doi:10.1515/9783110750294-025. ISBN 978-3-11-075029-4.

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